An organic light emission phenomenon is one of the examples converting current to visible light by an internal process of a specific organic molecule. The principle of an organic light emission phenomenon is as follows.
When an organic material layer is placed between an anode and a cathode and a voltage is applied between the two electrodes, electrons and holes are injected to the organic material layer from the cathode and the anode, respectively. The electrons and the holes injected to the organic material layer are recombined to form excitons, and light emits when these excitons fall back to the ground state. An organic light emitting diode using such a principle is generally formed with a cathode, an anode, and an organic material layer placed therebetween, which includes, for example, a hole injection layer, a hole transfer layer, a light emitting layer and an electron transfer layer.
Materials used in organic light emitting diodes are mostly pure organic materials or complex compounds in which organic materials and metals form complexes, and may be divided into hole injection materials, hole transfer materials, light emitting materials, electron transfer materials, electron injection materials and the like. Herein, as the hole injection material or the hole transfer material, organic materials having a p-type property, that is, readily oxidized and electrochemically stable when oxidized, are generally used. Meanwhile, as the electron injection material or the electron transfer material, organic materials having an n-type property, that is, readily reduced and electrochemically stable when reduced, are generally used. As the light emitting layer material, materials having both a p-type property and an n-type property, that is, having a stable form in both oxidized and reduced states, are preferable, and materials having high light emission efficiency converting, when excitons are formed, the excitons to light are preferable.
Accordingly, the development of organic light emitting diodes having high efficiency has been required in the art.